A technology of dealing with encryption of a printed matter is exemplified by a technology of, at first, segmenting a whole image into a plurality of blocks, rearranging images of the segmented blocks based on parameters obtained from an inputted password (encryption key), further black-and-white-inverting and mirror-inverting the images of the blocks designated by the parameters, and thus encrypting the images (refer to Patent document 1). On the occasion of decrypting the encrypted image, a positioning frame is attached to the outside of the image, and, after inputting the password (decryption key), the encrypted image is decrypted into the original image through procedures reversed to those for the encryption.
Another technology is that black-and-white squares having a predetermined size, which represent binary data, are arrayed in matrix and embedded into the printed matter (refer to Patent document 2). Further, for recognizing visualized positions on the occasion of decryption, positioning symbols are attached to predetermined positions of the matrix on the printed matter. Based on these positioning symbols, the image is captured by a scanner and a camera, and the embedded information is decrypted.
[Patent document 1] Japanese Patent Laid-Open Publication No. 8-179689
[Patent document 2] Japanese Patent Publication No. 2938338